Thermoform packaging machines and tray sealers configured for providing, by using vacuum and optionally also by using gas flushing, packages with very low residual oxygen values so as to guarantee a long durability, for example, in the case of foodstuffs, are known from the applicant's enterprise. In order to accomplish low residual oxygen values of less than 0.05%, it is normally necessary to evacuate the volume in the interior of the package to less than 10 mbar. For achieving this high vacuum value, a high performance of the vacuum pump and a long evacuation time are necessary. This has a negative influence on the performance of the packaging machine, since the number of producible packages per unit time decreases.
For increasing the performance of the packaging machine, a gas flushing system can additionally be used. In the case of such systems, the volume in the interior of the sealing station and of the package is evacuated to a value of, for example, 500 mbar and part of the oxygen is removed from the package in this way. The supply of gas causes a further displacement of the residual oxygen molecules from the interior of the package and leads to a further reduction of the residual oxygen value. The gas is supplied on one side of the package through gas flushing apertures in the sealing tool and discharged on the opposite side through evacuation apertures. A part of the gas volume flow flows in the upper area of the package from the gas flushing aperture side to the evacuation aperture side. Another part of the gas volume flow flows into the lower part of the package and from there upwards again. This results in a point of intersection of this gas volume flow and in flow losses caused by turbulences. This has a negative influence on the displacement of the oxygen molecules from the package. This combination is nevertheless advantageous, on the one hand, insofar as the processing time will be shorter than in cases where evacuation alone is used and, on the other hand, insofar as it is possible to provide packages having only a low vacuum and, consequently, a lower load on the package but nevertheless low residual oxygen values. If the product in question is meat, the package may, alternatively, also be flushed with a gas mixture of oxygen and carbon dioxide so as to establish an oxygen content of 30 to 50%. The high oxygen content ensures an enduring red color of the meat and the carbon dioxide content provides durability.